The best Japanese AAA gun of World
War II, whose characteristics can only be described as "superb."
Their only fault was a rather short service life, the result of high muzzle
velocity and a fast rate of fire. In 1945, most new production mounts
were diverted to shore-based installations.

There were two versions of the gun barrel.
Model Type I used a radially expanded, removable lining while the Model
Type I2 was of monobloc construction. Both types had breech
rings and a horizontal sliding breech-block. Spring-operated, semi-automatic
rammers, which were cocked by the recoil force, were mounted above the
guns. These allowed the guns to be loaded at any angle of elevation,
an important factor for any AA weapon. Shells were manually inserted
into fuze setting machines before being placed into the loading trays.

A total of 169 guns were completed between
1940 and 1944 with 68 used in land mountings. All were in twin mounts.

Two mountings were removed from Natsuzuki
at the end of the war and sent to the USA for examination.

A new 10 cm (3.9") Type 5 (Model 1945)
gun was under design at the end of the war, but no guns are known to have
been completed. It was intended that this gun would be a replacement
for the 12 cm (4.7") 10th Year Type
used on escort vessels.

Destroyer Hatsuzuki in June 1944The 10 cm (3.9") guns are in the four
main twin mountsIWM Photograph

Destroyer HanazukiHanazuki was transfered to the USN in
1947 and then designated as DD-934. She was sunk as target on 3 February
1948.

.

Gun Characteristics

.

Designation

10 cm/65 (3.9") Type 98 (Model 1938)

Ship Class Used On

Akitsuki, Oyodo, Taiho and B-64 classes

Date Of Design

1938

Date In Service

1942

Gun Weight

6,731 lbs. (3,053 kg)

Gun Length oa

265.0 in (6.730 m)

Bore Length

255.9 in (6.500 m)

Rifling Length

221.7 in (5.631 m)

Grooves

(32) 0.49 in deep x 0.219 in (1.25 mm
x 5.565 mm)

Lands

0.167 in (4.252 mm)

Twist

Uniform RH 1 in 28

Chamber Volume

641 in3 (10.5 dm3)

Rate Of Fire

15 - 21 rounds per minute

.

Ammunition

.

Type

Fixed

Weight of Complete Round

HE - 61.7 lbs. (28 kg)

Projectile Types and Weights

HE - 28.67 lbs. (13 kg)

Bursting Charge

2.1 lbs. (0.95 kg)

Projectile Length

16.1 in (41 cm)Complete Round: 44 in (111.8 cm)

Propellant Charge

13.2 lbs. (6 kg) 30 DC (?)Cartridge - 33 lbs. (15 kg)

Muzzle Velocity

3,281 fps (1,000 mps)

Working Pressure

19.4 tons/in2 (3,050 kg/cm2)

Approximate Barrel Life

350 - 400 rounds

Ammunition stowage per gun

about 400 rounds on larger shipsOyodo: 200 roundsAkitsuki: N/A

Note: It is interesting
to note that the Japanese apparently never developed incendiary shrapnel,
ASW or even illumination rounds for this weapon, implying that it was solely
intended for use as an AA gun. Practice shells were provided.

2) Mountings used electro-hydraulic power.
Power was supplied by a 15 hp electric motor operating from 220 Vdc and
which ran at 600 rpm.

3) Akizuki class used two dredger hoists
to supply ammunition to the working chamber. From here, rounds were
manhandled to loading positions for pusher hoists, one for each gun.
At the top of the hoists, rounds automatically rolled to waiting positions
where shell passers handed them to loaders standing on the gun platform,
which moved with the guns. Fuze-setting machines were attached to
the breech faces of the guns. Loading trays were manually operated.

4) The Oyodo class used four bucket hoists
which delivered ammunition from the magazines to a working chamber abaft
the No. 2 15.5 cm (6.1") gun barbette.
The maximum rate of supply was 20 to 22 shells per minute per hoist.
The ammunition was then carried by hand to the 10 cm (3.9") gun mounts,
which were 77 and 135 feet (22 and 41 m) further aft. There were
ready-use ammunition storage lockers near the weapon mountings which allowed
for a higher rate of fire for a period of time. The fuze setting
on this class was done by a separate machine before the shells were loaded
into the gun.

5) Ramming was via a spring-powered mechanism
that was cocked by the recoil force when the gun fired. The mechanism
had a removable pulley arrangement where the gun was depressed to cock
the rammer for the first round. A misfire meant that the subsequent
round needed to be rammed by hand, unless there was time to reattach the
pulley and cycle the gun elevation. The rammer was similar to that
in the earlier 12.7 cm/40 Type 89, but
embodied some improvements, mainly in the tripper gear which had an improved
type of tumbler release mechanism. Early production rammers suffered
frequent failures due to fracturing of the rammer heads, but this problem
was overcome and they gave good service during most of the war.

6) Distance between gun axes was 26.0 inches
(66 cm).

.

Data from"Japanese Warships of World War II" by
A.J. Watts"Naval Weapons of World War Two" by John
Campbell"Japanese Cruisers of the Pacific War"
by Eric Lacroix and Linton Wells II"Battleships: Axis and Neutral Battleships
in World War II" by W.H. Garzke, Jr. and R.O. Dulin, Jr."The Japanese Ships of the Pacific War"
by The Koku-Fan---US Naval Technical Mission to Japan report
O-19: Japanese Projectiles General TypesUS Naval Technical Mission to Japan report
O-47(N)-1: Japanese Naval Guns and Mounts-Article 1, Mounts Under
18"
Page History

26 August 2007 - Benchmark26 December 2011 - Added information about
the 10 cm Type 527 May 2012 - Updated to latest template09 August 2014 - Added comment about mountings
from Natsuzuki being sent to USA